1. Field of the Invention
The present invention relates to an accommodating intraocular lens implant (IOL), containing a refractive material therein, for surgical replacement of the natural crystalline lens to treat refractive errors in the human eye.
2. Description of the Prior Art
Refractive errors in the eye affect one's ability to properly focus an image upon the retina due to a change in the refractive medium of the eye, e.g., the cornea, the natural crystalline lens, or both. The refractive errors pertinent to this application include myopia, hyperopia, and presbyopia. A myopic lacks the ability to focus an image located at a distance from the viewer because the cornea has become elongated, thereby increasing the eye's focal length. A hyperopic lacks the ability to focus on objects located near the viewer because the cornea is not elongated enough or is too flat, and cannot refract light properly upon the retina. Instead, light entering the eye does not bend sharply enough to focus upon the retina. In contrast to myopia wherein the image is brought to focus in front of the retina, hyperopia causes the image to focus behind the retina. Presbyopia is another type of refractive error which results in the inability of the eye to focus because of hardening of the natural crystalline lens. The hardened natural crystalline lens prevents focusing upon objects located near to the viewer. Presbyopia occurs in conjunction with myopia or hyperopia.
The known treatment varies with the type of refractive error to be corrected. Each of the refractive errors may be corrected by external spectacle lenses. Also, refractive surgery is known in the art for correcting the aforementioned refractive errors, and includes radial keratotomy, astigmatic keratotomy, photoreflective keratectomy, and laser in situ keratomileusis (LASIK). Each of the refractive surgical methods mentioned above involve making multiple incisions into the cornea in order to reshape it. Possible side effects of refractive surgery include irregular astigmatism, infection, or haze formation which could result in permanent changes in the cornea and possible loss of best-corrected visual acuity. A possibility of under or over correction also exists with the aforementioned refractive surgeries. Furthermore, none of these refractive surgeries can be used to correct all of the above-referenced refractive errors.
Various IOLs have been used to treat cataracts. The first implant of an IOL within the eye to treat cataracts occurred in 1949. This experimental surgery attempted to place the replacement lens in the posterior chamber of the eye behind the iris. Problems such as dislocation after implantation forced abandonment of this approach, and for some period thereafter IOLs were implanted in the anterior chamber of the eye.
Others returned to the practice of inserting the IOL in the area of the eye posterior to the iris, known as the posterior chamber. This is the area where the patient's natural crystalline lens is located. When the IOL is located in this natural location, substantially normal vision may be restored to the patient, and the problems of forward displacement of the vitreous humor and retinal detachment encountered in anterior chamber IOLs are less likely to occur. IOLs implanted in the posterior chamber are disclosed in U.S. Pat. Nos. 3,718,870, 3,866,249, 3,913,148, 3,925,825, 4,014,049, 4,041,552, 4,053,953, and 4,285,072. None of these IOLs have accommodation capability.
IOLs capable of focusing offered the wearer the closest possible substitute to the natural crystalline lens. U.S. Pat. No. 4,254,509 to Tennant discloses an IOL which moves in an anterior direction upon contraction of the ciliary body and which is located anterior to the iris. Although the Tennant IOL claims to possess accommodation capabilities, it presents the same disadvantages as other anterior chamber lenses. U.S. Pat. No. 4,253,199 to Banko approaches the problem of providing a focusable IOL in a different manner, by providing a replacement IOL of deformable material sutured to the ciliary body. This IOL functions in much the same manner as the natural crystalline lens, but may cause bleeding because it requires sutures.
U.S. Pat. No. 4,409,691 to Levy claims to provide an accommodating IOL positioned within the capsule. This IOL is located in the posterior area of the capsule and is biased toward the fovea or rear of the eye. The Levy IOL is deficient because it requires the ciliary muscle to exert force through the zonules on the capsule in order to compress the haptics inward and drive the optic forward for near vision. However, the ciliary muscles do not exert any force during contraction because the zonules, being flexible filaments, exert only tension, not compression on the capsule. The natural elasticity of the IOL causes the capsule to become more spherical upon contraction of the ciliary muscle. Thus, there is no inward force exerted on the capsule to compress the haptics of the Levy IOL, and therefore accommodate for near vision. Even if such force were somehow available, the Levy IOL's haptics are loaded inward when accommodating for near vision. Since accommodation for near vision is the normal status of the capsule, the Levy IOL's haptics are loaded, reducing the fatigue life of the springlike haptics.
U.S. Pat. No. 5,674,282 to Cumming is directed towards an allegedly accommodating IOL for implanting within the capsule of an eye. The Cumming IOL comprises a central optic and two plate haptics which extend radially outward from diametrically opposite sides of the optic and are movable anteriorly and posteriorly relative to the optic. However, the Cumming IOL suffers from the same shortcomings as the Levy IOL in that the haptics are biased anteriorly by pressure from the ciliary bodies. This will eventually lead to pressure necrosis of the ciliary body.
Finally, U.S. Pat. No. 4,842,601 to Smith discloses an allegedly accommodating IOL having anterior and posterior members which urge against the anterior and posterior walls of the capsule. The muscular action exerted on the capsule will cause the IOL to flatten, thereby changing the focus thereof. The Smith IOL is formed of first and second plastic lens members connected to one another adjacent their peripheral edges so as to provide a cavity therebetween. The connection between the lens members is accomplished by way of a U-shaped flange on the first member which forms an inwardly facing groove for receiving an outwardly extended flange on the second member. The Smith IOL is faulty because the structure of the lens members makes surgical implantation thereof extremely difficult to accomplish, even for highly skilled surgeons. Furthermore, the Smith IOL requires sutures which increases the risk of bleeding.
The IOLs discussed above replaced the opaque crystalline lens symptomatic of cataracts through a small incision in the iris and anterior wall of the biological capsule. The IOLs for the treatment of cataracts differed from the present invention in that the present invention utilizes a highly refractive material to compensate for defects in the eye's natural refractive media, e.g, the cornea and the natural crystalline lens.
There is a great need in the art for a lightweight IOL which can be used to correct a variety of refractive errors in conjunction with other eye defects which require replacement of the natural crystalline lens, such as cataracts. This IOL should be readily insertable into the capsule and should last for a substantial number of years without damaging any of the eye components.